Mechanical amplitude transformer

ABSTRACT

A mechanical amplitude transformer for use with sonic or ultrasonic energy comprises two members of different density material joined to each other by a metallurgical bond and dimensioned to operate as a half wavelength resonator when energized with energy of predetermined frequency.

United States Patent Inventors Everett A. Harris;

Stanley E. J acke, both of Ridgefield, Conn.

33,637 May 1, 1970 Dec. 14, I971 Branson Instruments, Incorporated Stamford, Conn.

App]. No. Filed Patented Assignee MECHANICAL AMPLITUDE TRANSFORMER 9 Claims, 6 Drawing Figs.

U.S. Cl 310/82, 310/87 310/26 int. Cl H0lv 7/00 FieldolSearch 3l0/8,8.l,

lg GENERATOR References Cited UNITED STATES PATENTS 2,792,674 5/1957 Balamuth et al 310/26 x 2,947,889 8/1960 Rich 310/26 2,947,886 8/1960 McGunigle..... 310/83 3,304,479 2/1967 Kleesattel et al 3 l0/26 X 3,175,406 3/1965 Eisner 3l0/8.7X 2,680,333 6/1954 Calosl 310/26x Primary Examiner-D. X. Sliney Assistant Examiner-B. A. Reynolds Attorney-Ervin B. Steinberg ABSTRACT: A mechanical amplitude transformer for use with sonic or ultrasonic energy comprises two members of different density material joined to each other by a metallurgical bond and dimensioned to operate as a half wavelength resonator when energized with energy of predetermined frequency.

HIGH Fneousncy I4 \IO 2 Sheets-Sheet 1 HIGH FREQUENCY GENERATOR CONVERTER UCJ MECHANICAL AMPLITUDE |e TRANSFORMER EVERETT A.HA RRIS STANLEY E. JACKE INVENTORS.

Patented Dec. 14, 1971 3,628,011

2 Sheets-Sheet 2 F I G. 4

MECHANICAL INSTANTANEOUS 22 STRESS AMPLITUDE v. LOCATION v v. LOCATION EVERETT A. HARRIS STANLEY E. JACKE HINVENTORS.

The design of mechanical amplitude transformers is well understood in the art and the transformer comprises generally an elongated member which constitutes the coupling member for transmitting energy between a source of sonic energy and a workpiece. Responsive to the application of mechanical vibration at an input end of the coupling member, the output member transmits such energy to a workpiece. In order to obtain increased amplitude of vibration at the output end, the coupling member generally is provided along its length with a change in cross-sectional area, and the mechanical amplitude transformer then becomes known, for instance, as a double cylinder or step born, a catenoidal horn, tapered horn, exponential horn and the like.

The mechanical amplitude gain which can be obtained from a particular resonator is dependent on the mechanical stress of the material which, in turn, is not only a function of the material itself, but also of the cross-sectional area. For instance, a high mechanical gain is obtainable from the so-called step horn design which is machined in such a manner that the change in cross-sectional area occurs in the nodal region of longitudinal motion. While a sharp or abrupt step in this region shows maximum gain, assuming a given change in crosssectional area, it will be apparent that a radius or gradual change in cross-sectional area must be provided in order to avoid a high stress concentration which under stressed condition would cause the material to rupture. Materials used for a mechanical amplitude transformer may comprise high-stress aluminum, titanium, or Monel.

The present invention concerns an improvement in the design of a mechanical amplitude transformer by using dissimilar materials, specifically using two materials having different density.

The prior art discloses piezoelectric transducers wherein the piezoelectric material, usually in the form of a flat wafer, is sandwiched between two metal sections having different densities, see for instance Julian R. Frederick supra, pages 67 through 69 and 74, or U.S. Pat. No. 2,947,889 dated Aug. 2, 1960 issued to S. Rich. Transducer constructions of this type show an improved performance and are fairly common, particularly in conjunction with ultrasonic cleaning apparatus where these transducers are coupled to the bottom or to the sidewall of a tank which is filled with a liquid. Upon energizing the piezoelectric material with high frequency energy, the transducers are caused to vibrate and to transmit the vibratory energy to the liquid confined in the tank.

The present invention is a certain extension of the previous teaching and provides a transmitting or coupling member for ultrasonic energy which is characterized by a mechanical gain in transmitting sonic energy from one location to another location without necessitating, under certain conditions, a change in cross-sectional area as has been known heretofore.

One of the principal objects of this invention is, therefore, the provision of a new and improved mechanical amplitude transformer for transmission of sonic or ultrasonic energy.

Another important object of this invention is the provision of a mechanical amplitude transformer which exhibits a gain in mechanical amplitude without the necessity of providing a change in cross-sectional area.

Another important object of this invention is the provision of a mechanical amplitude transformer updated to operate as a half wavelength resonator and comprising two members joined to each other by a metallurgical bond, the members being of substantially equal and uniform cross-sectional area.

A further important object of this invention is the provision of a mechanical amplitude transformer which exhibits a larger output diameter, greater flexural and torsional rigidity, and lower stress concentration than a transformer providing the same or similar performance, but made from a single density material.

Further and still other objects of this invention will be more clearly apparent by reference to the following description, when taken in conjunction with the accompanying drawing, in which:

. FIG. 1 is a schematic illustration of a typical sonic or ultrasonic apparatus which includes a mechanical amplitude transformer;

FIG. 2 is a vertical view of the mechanical amplitude transformer in accordance with the improved design;

FIG. 3 is a graph of instantaneous mechanical stress v. location for the design per FIG. 2;

FIG. 4 is a graph of the instantaneous motional amplitude v. location for the design per FIG. 2;

FIG. 5 is a vertical view ofan alternative design, and

FIG. 6 is a vertical view of a mechanical amplitude transformer showing a further alternative embodiment. Referring now to the figures and FIG. 1 in particular, there is shown a generator 10 which supplies high frequency electrical energy via a cable 12 to a converter unit 14. The converter unit 14 includes either piezoelectric means or magnetostrictive means (not shown) for converting the applied high frequency electrical energy to mechanical vibration which is apparent at an output end 16. The converter unit, in a preferred embodiment, may be constructed in accordance with the teachings disclosed in US. Pat. No. 3,328,610 issued to S. E. Jacke et al., dated June 27, 1967 entitled Sonic Wave Generator." Typically, a converter unit of this type is designed for operation at a frequency of 20 kHz., but similar units are available for operation at a lower frequency, for instance 18 kHz. and for operation at a higher frequency, such as 60 kHz. In order to apply the vibrations provided by the converter unit 14 to a workpiece, it is common practice to use a coupling member or a mechanical amplitude transformer 18 of elongate shape, which by means of a stud 20 is mechanically coupled to the output surface 16 of the converter unit 14. Hence, the transformer 18 receives the vibrational energy at its upper radial surface and is adapted to be coupled with its output surface 22 to a workpiece which may be a solid or a liquid. The mechanical amplitude transformer or horn 18 must be dimensioned so that it is resonant at the applied frequency and in order to accomplish this, its length must substantially be equal to an integer of half wavelengths of the sound traveling longitudinally through the material forming the resonator.

As indicated heretofore, in order to obtain an increase of mechanical motion at the output surface 22, it has been common practice to achieve this by fabricating the transformer 18 from aluminum, titanium or Monel metal and provide a reduction in cross-sectional area between the input surface and the output surface.

The present and improved design is shown in FIG. 2. The transformer, an elongate member, is made of two members, an upper member 18A and a lower member 188 which are joined to each other by a metallurgical bond 24. The bond 24 is located at the nodal region of longitudinal motion. More specifically, the upper portion 18A and the lower portion 183 are materials of different density and modulus of elasticity. The lower portion 188, or output portion, is the material having the lower density. Both members are joined to each other by friction or inertia welding so as to provide a metallurgically sound bond and form a unitary assembly. This is a particularly important feature since the nodal region is subjected to maximum mechanical stress as is clearly apparent from the graph per FIG. 3.

As shown in FIG. 2, the member 18A and member 188 are of equal and uniform cross-sectional area and if both were made of the same metal, there would be no mechanical amplitude gain between the input end and the output end. Assuming, however, that in accordance with this invention the member 18A is made of steel or brass and the member 188 is made of high-stress aluminum, a mechanical amplitude gain of about three between the input end and the output end is obtained as clearly seen in FIG. 4.

Thus, it will be apparent that a mechanical amplitude gain is available without the necessity of a cross-sectional change which, as it readily is apparent to those skilled in the art, has a detrimental effect upon the flexural and torsional rigidity of the resonator and increases the stress concentration in an area which already undergoes maximum stress.

In another preferred embodiment, a mechanical amplitude gain is obtained under the condition of constant cross-sectional area if the rear member is made of titanium and the front member of aluminum.

In order to increase the mechanical gain still further, the above disclosed construction of the mechanical amplitude transformer may be combined with a reduction in cross-sectional area as by providing a stepped design, FIG. 5, or an exponential or a catenoidal design as indicated in FIG. 6. The

combination of different density materials and cross-sectional change, of course, provides a transformer having a high gain and improved mechanical rigidity and stress bearing capacity when compared with the heretofore known constructions.

However, the main advantage of the present transformer design resides in the fact that a mechanical amplitude gain is available without reduction in cross-sectional area and, thus, horns of considerably greater rigidity and load bearing capacity can be constructed.

What is claimed is:

l. A mechanical amplitude transformer adapted to receive vibratory energy at one end surface and provide vibratory energy of increased motional amplitude to a workpiece at an opposite end surface comprising:

a first elongate metal member having a certain density;

a second elongate metal member having a density different from that of said first member;

a metallurgical bond joining said members to each other to provide a unitary assembly, and

the composite length of said members being dimensioned for causing said transformer to be resonant as a half wavelength resonator at a predetermined frequency of the vibrations transmitted longitudinally through said unitary assembly.

2. A mechanical amplitude transformer as set forth in claim 1, said metallurgical bond being disposed substantially in the nodal region of longitudinal motion occurring in said transformer.

3. A mechanical amplitude transformer as set forth in claim 2, one of said members being aluminum.

4. A mechanical amplitude transformer as set forth in claim 2, one of said members being titanium.

5. A mechanical amplitude transformer as set forth in claim 2, said members being of substantially constant cross-sectional area.

6. A mechanical amplitude transformer as set forth in claim 2, said transformer having a change in cross-sectional area.

7. A mechanical amplitude transformer as set forth in claim 2, said transformer having a change in cross-sectional area occurring substantially in the nodal region of longitudinal motion occurring in said transformer.

8. A mechanical amplitude transformer as set forth in claim 2, the member having the lower density of said two members being adapted to transfer vibratory energy to the workpiece.

9. A mechanical amplitude transformer as set forth in claim 2, said first elongate metal member being steel and said second elongate metal member being aluminum.

I! i i 

1. A mechanical amplitude transformer adapted to receive vibratory energy at one end surface and provide vibratory energy of increased motional amplitude to a workpiece at an opposite end surface comprising: a first elongate metal member having a certain density; a second elongate metal member having a density different from that of said first member; a metallurgical bond joining said members to each other to provide a unitary assembly, and the composite length of said members being dimensioned for causing said transformer to be resonant as a half wavelength resonator at a predetermined frequency of the vibrations transmitted longitudinally through said unitary assembly.
 2. A mechanical amplitude transformer as set forth in claim 1, said metallurgical bond being disposed substantially in the nodal region of longitudinal motion occurring in said transformer.
 3. A mechanical amplitude transformer as set forth in claim 2, one of said members being aluminum.
 4. A mechanical amplitude transformer as set forth in claim 2, one of said members being titanium.
 5. A mechanical amplitude transformer as set forth in claim 2, said members being of substantially constant cross-sectional area.
 6. A mechanical amplitude transformer as set forth in claim 2, said transformer having a change in cross-sectional area.
 7. A mechanical amplitude transformer as set forth in claim 2, said transformer having a change in cross-sectional area occurring substantially in the nodal region of longitudinal motion occurring in said transformer.
 8. A mechanical amplitude transformer as set forth in claim 2, the member having the lower density of said two members being adapted to transfer vibratory energy to the workpiece.
 9. A mechanical amplitude transformer as set forth in claim 2, said first elongate metal member being steel and said second elongate metal member being aluminum. 